Radio haloes in nearby galaxies modelled with 1d cosmic ray transport using SPINNAKER

Abstract

We present radio continuum maps of 12 nearby (D ≤ 27 Mpc), edge-on (i ≥ 76?), latetypespiral galaxies mostly at 1.4 and 5 GHz, observed with the Australia Telescope CompactArray, Very LargeArray, Westerbork Synthesis Radio Telescope, Effelsberg 100-m, and Parkes64-m telescopes. All galaxies show clear evidence of radio haloes, including the first detectionin the Magellanic-type galaxy NGC 55. In 11 galaxies, we find a thin and a thick discthat can be better fitted by exponential rather than Gaussian functions. We fit our SPINNAKER(SPectral INdex Numerical Analysis of K(c)osmic-ray Electron Radio-emission) 1D cosmicray transport models to the vertical model profiles of the non-thermal intensity and to thenon-thermal radio spectral index in the halo. We simultaneously fit for the advection speed (ordiffusion coefficient) and magnetic field scale height. In the thick disc, the magnetic field scaleheights range from 2 to 8 kpc with an average across the sample of 3.0 ± 1.7 kpc; they showno correlation with either star formation rate (SFR), SFR surface density (Σ SFR), or rotationspeed (Vrot). The advection speeds range from 100 to 700 km s-1 and display correlations ofV α SFR0.36±0.06 and V α Σ0.39±0.09 SFR; they agree remarkably well with the escape velocities(0.5 ≤ V/Vesc ≤ 2), which can be explained by cosmic ray-driven winds. Radio haloes showthe presence of disc winds in galaxies with ΣSFR &gt; 10-3Mo˙yr-1 kpc-2 that extend overseveral kpc and are driven by processes related to the distributed star formation in the disc.</p